The Significance of Surface Changes on Explanted Polyurethane Pacemaker Leads

Although over 140,000 polyurethane leads have been implanted in humans, a controversy has recently arisen dealing with the significance of frequently detected irregularities on explanled insulator surfaces by scanning electron microscopy (SEM), and their relationship with lead failure. We therefore implanted ten, 6 Fratrial polyurethane leads and an equal number of 4 Fr ventricular leads in dogs for a mean 26 ± 2 and 29 ± 2 weeks, respectively. Fourteen leads were removed utilizing metered force. The remaining leads were removed surgically without force at the termination of the study. Specimens were stored in saline prior to physical testing (tensile strength and elongation) of intravascular and extravascular lead segments. Similarly stored samples were prepared for SEM analysis. The polyurethane insulator disconnected from the electrode on forcible removal in three atrial and two ventricular leads (concordant connected from the electrode on forcible removal in three atrial and two ventricular leads (concordant for two pairs). There was no significant relationship between the results of physical testing and extraction force, lead size, integrity on removal, sample location or SEM scores. Chemical analysis of surface changes employing both x-ray and electron emission spectroscopy failed to reveal evidence of protein adsorption or liquid impregnation. Samples soaked in sodium hydroxide displayed the same SEM irregularities. The combined effects of fissuring and fluid absorption by polyurethane did not affect chronic anodal or cathodal thresholds, in conclusion, a clear relationship between chronic surface irregularities and the insulator function of polyurethane, its integrity in situ, or its strength atexplanthas not been established by this relatively short-term study. On the other hand, a potential time-dependent impact of these changes on lead performance has not been excluded. Moreover, only a single species of medical grade polyurethane has been clinically evaluated. Thus, the ultimate place of polyurethane leads in pacing systems hasyet to be determined.     

Long-Term Comparison of the Electrical Characteristics of Polyurethane and Polyethylene Insulated Ventricular Leads

Two types of pacing leads with different insulation material, polyurethane, and polyethylene, were followed for 44 months with respect to their electrophysiological characteristics and complications. In 48 patients, 32 polyurethane leads (Lifeline 493-03) and 16 polyethylene leads (EMT 588 D) were implanted and connected in all cases to the same type of programmable ventricular inhibited (VVI) pulse generator (Programalith, Pacesetter). There was a significant fall during the follow-up in lead impedance with the polyurethane leads (495 +/- 62 to 444 +/- 58 ohms, P less than 0.01), whereas the corresponding measurements for the polyethylene leads were essentially unchanged (360 +/- 58 to 378 +/- 71 ohm, ns). The energy of the stimulation threshold tended to increase in the polyurethane group, whereas an opposite tendency was observed in the polyethylene group. Pacing and/or lead failures were not observed in any case. The observed fall in impedance with the polyurethane leads was seemingly of no clinical significance.     

Survival of Implantable Pacemaker Leads

FURMAN, S., ET AL.: Survival of Implantable Pacemaker Leads. Early polyurethane leads were reported to have a high incidence of materials failure. In 1979 a six-center registry was begun. By October 31, 1989, 7, 311 leads had been registered and lead longevity was calculated by individual manufacturer, cumulatively for all manufacturers and for individual leads. Each lead was registered at implant and at removal from service as having been removed for materials failure or for unrelated reasons. Calculations were made for 23 models and for a total of three manufacturers with more than 100 leads implanted. Four thousand seven hundred and sixty three leads (65.1%) were from Medtronic; 2, 177 (29.8%) from Cordis; 297 (4.1%) from Intermedics; and 77 (1.0%) were from all others. The 10-year cumulative survival of Medtronic leads was 96.6 ± 0.4%; for Cordis leads it was 99.9 ± 0.1% and for Intermedics leads 97.7 ± 0.9%. Three lead models registered over 100 units and had poorer survival at 5 years than the remainder of all manufacturers' experience. They were #6972 (n = 107) with 78.6 ± 4.5%; #6991U (n = 294) with 90.6 ± 1.9%; and #4012 (n = 288) with 97.3 ± 1.5%. Other possibly failed models did not achieve statistical significance. It can be anticipated that a lead which survives to the seventh year will have prolonged longevity as thereafter additional failures are uncommon.     

Surgical Removal of Infected Transvenous Pacemaker Leads

Infection, though uncommon, can be the most lethal of all potential complications following transvenous pacemaker implantation. Eradication of infection associated with pacemakers requires complete removal of all hardware, including inactive leads. Since 1972, 5,089 patients have had 8,508 pacemaker generators implanted at Montefiore Medical Center. There were 91 infections (1.06%); four of our patients required surgical removal. Nine additional patients were referred for surgical removal of infected transvenous pacemaker leads from other institutions. Surgical methods for removal included use of cardiopulmonary bypass or inflow occlusion. Surgery may be safely used in unstable or elderly patients and should not be reserved as a last resort. This article reviews our surgical experience removing infected pacemaker leads at Montefiore Medical Center.     

Intravascular Extraction of Chronic Pacemaker Leads: Efficacy and Follow-Up

Extraction of chronic pacemaker leads has been recommended for infections, prevention of venous thrombosis, migration, and possible perforation. Success with constant traction techniques has been variable, and the cost and morbidity of open chest surgical procedures are prohibitive. Efficacy of a new system for lead extraction using intravascular techniques was analyzed. The system (Cook Pacemaker) uses a locking stylet, which is secured at the distal electrode by counterclockwise rotation to reinforce the lead and facilitate traction, and dilator sheaths that are used to free the lead from adhesions in the venous system. In a series of 56 patients (ages 19–88)who presented for lead extraction because of erosion (5), infection (14), lead replacement (35), or other (2), 86 leads were extracted. Thirty-two were atrial leads and 54 ventricular; 23 had active fixation and 63 passive. Average duration of implant was 58 ±42 months (range 1–264). Eighty-four leads were totally removed and two partially removed. For these two leads, the distal tip was not removed; in both cases the locking stylet was not secured at the distal electrode due to obstruction within the lead. Two patients developed arm edema following the procedure, which resolved with elevation. One patient developed a subclavian thrombosis, which resolved with warfarin anticoagulation. Four patients have expired due to unrelated causes. In conclusion, this intravascular approach for extraction of chronic leads is effective, and the procedure is safe when performed by experienced personnel.     

First European Experience Using Excimer Laser for the Extraction of Permanent Pacemaker Leads

An Excimer Laser system for the extraction of permanent pacemaker leads has been developed by Spectranetics Inc. and Dr. Charles L. Byrd. The laser energy is emitted at the tip of a flexible, fiberoptic 12F sheath that permits the removal of leads with a max outer diameter of 7.1F. The CVX-300 Excimer Laser source is a xenon chloride laser with an output of 308 nm not visible to the human eye. This cool cutting laser has an absorption depth of 0.06 mm, the energy being absorbed by proteins and lipids. In clinical practice this means that the fibrotic sheaths usually surrotinding the leads can be cut without damaging the endothelial wall or the insulation of leads, due to these characteristics the sheath can, however, not pass over tines. For the freeing of lead tips, locking stylets and outer sheaths are combined to perform counter traction. Results: From 8/96 to 5/97 50 leads (38 atrial, 12 ventricular) from 45 patients (22 females, 23 males, mean age 65.1 years, range 32–94) were extracted using the Excimer Laser at our institution. Mean lead implantation time was 47.7 months (range 10.5–351.7). Indication for extraction was suspected J-wire fracture in 16 leads, prophylactic in 8 leads, infection in 12 leads, exit block in 4 leads and other reasons in 10 leads. Mean extraction time, excluding reimplantation, was 10 minutes (range 1–50). The objective of the procedure (normally complete lead removal) was accomplished in all cases but three. All intended lead replacements were successful. No complications occurred. All patients left the hospital in good condition, one patient died, within 30 days due to progressive heart failure. Conclusions: Lead extraction with Excimer Laser seems to be a safe and efficacious procedure. However, due to the inherent risks appropriate training and experience are essential. If the initial promising results can be maintained, indications for the removal of permanent pacing leads may widen considerably.     

Comparative Thrombogenicity of Pacemaker Leads

To evaluate the throm bogenicity of transvenous silicone and polyurethane pacemaker leads, 9 of 12 anesthetized Yorkshire pigs (27–32 kg) were implanted with silicone (n = 5) or polyurethane (n = 4) pacemaker leads via a femoral vein. The remaining three pigs served as controls. All 12 pigs were injected with autologous indium-111 labeled platelets (300–420 μCi) 24 hours before anesthesia induction. The pigs were monitored for 3 hours under a gamma camera. Radioactivity in blood and lead segments was measured with a gamma counter. Platelet deposits were denser on silicone leads (441.58 ± 915.0 to 2.19 ± 2.07) than on polyurethane leads (1.21 ± 1.33 to 0.27 ± 0.14) (P > 0.05). Denser platelet deposits were detected at the tip of all leads. Density of platelet deposits declined from tip to distal segments in silicone leads. The percentage of injected platelet radioactivity in the lungs of pigs with either silastic leads (12.9 ± 2.3%) or polyurethane leads (10.1 ± 2.2%) was higher than in the controls (4.6 ± 0.5%) (P < 0.05). This difference indicates thrombus formation and embolization in the lungs early after lead implantation. Thrombogenicity of polyurethane leads may be lower than that of silicone leads.     

Long-Term Performance of Polyurethane Pacing Leads: Mechanisms of Design-Related Failures

Environmental stress cracking has been identified as a crack propagating mechanism in polyurethane-insulated, heart pacemaker leads, which is directly related to specific lead design parameters. Lead designs imposing excessive stress on the polyurethane insulation through an interference fit between the coil and polymer have demonstrated insulation failures. Conversely, low-stress designs have shown virtually no insulation problems. The higher-stress designs have used organic solvents to facilitate coil placement during manufacturing. which may result in lowering the polymer's ability to resist the higher stress. In addition, a specific silver-containing coil wire composition has been found to galvanically corrode upon body fluid intrusion info the lead, ionizing the silver. These ions interact with the polyurethane polymer resulting in the loss of polymer strength. All polyurethane lead failures to date have been specific to high stress and/or chemical interaction. Leads using low-stress designs and nonreactive coil wire compositions continue to demonstrate a positive clinical experience.     

Paired Comparisons of Steroid-Eluting and Nonsteroid Endocardial Pacemaker Leads in Dogs: Electrical Performance and Morphologic Alterations

The effects of steroid elution from endocardial pacemaker electrodes on electrical performance and the thickness and cellularity of the reactive fibrous connective tissue formed around the stimulating electrode (peri-electrode tissue) were determined. Comparison was made with a nonsteroid electrode implanted in the same cardiac chamber (right ventricle) in each of six dogs for 6 weeks. Paired Students' t-tests showed that steroid-eluting leads had significantly (P less than .05): (1) lower voltage stimulation thresholds (as determined in sequential measurements made on the conscious animals during the experiment and on the anesthetized dogs at termination of the study); (2) less fibrous connective tissue formation around the electrode surfaces; and (3) fewer cells per unit area of peri-electrode fibrous connective tissue. There were also fewer (P less than .10) mast cells in the reactive connective tissue surrounding steroid-eluting leads. The thinner reactive connective tissue surrounding the steroid-eluting electrodes was correlated with lower voltage stimulation thresholds (r = 0.7, P less than .01). This is consistent with the hypothesis that the effect of the peri-electrode connective tissue is to increase the virtual surface area of the electrode, decreasing current density in adjacent stimulatable tissue. The relatively fewer total cells and mast cells in the peri-electrode connective tissue of the steroid-eluting electrodes suggest that the observed differences in fibrous connective tissue thickness, and therefore voltage stimulation threshold, may be related to a relatively decreased population of inflammatory cells due to the anti-inflammatory properties of the steroid.     

Assessment of the Subclavian Vein in Patients with Transvenous Pacemaker Leads

Thrombosis of the subclavian vein can occur after the implantation of transvenous pacemaker electrodes. Although this is seldom followed by thromboembolic complications, it can cause problems when replacing the leads. To assess the impact of the pacemaker leads on the subclavian vein, a study using nonin-vasive duplex sonography was performed on 56 patients at an average of 41 months after the implantation. Forty-three percent of the patients were found to have a normal function of the subclavian vein, 46% developed pathological changes of the vessel wall, and 11% occluded. These changes rarelv caused symptoms, and, therefore, had little clinical significance. Moreover, the occlusion rate was found independent of the patient's age, the patient's sex, the number of electrodes, the procedure of implantation, and even the time from implantation. As a result, the clinical diagnosis of occlusion is uncertain. Therefore, duplex sonography is recommended as an easy means of excluding a totally thrombosed subclavian vein prior to replacing pacemaker leads.     

Recurrent Pulmonary Embolization Following Implantation of Transvenous Pacemaker

A 44-year-old man developed recurrent pulmonary embolization after implantation of a permanent transvenous DVI pacemaker connected to polyurethane leads. Thrombus was found in the left innominate and subclavian veins around the pacemaker leads, but not in the right atrium or in the venous system of the pelvis and the lower extremities. The recurrence of pulmonary embolization followed discontinuation of treatment with Coumadin. This case demonstrates that lifelong anticoagulation is indicated in patients who have had pulmonary embolization and/or venous thrombosis around the pacemaker leads.     

Comparison of Two Myoepicardial Pacemaker Leads: Follow-up in 80 Children, Adolescents, and Young Adults

Although several types of commercially available epicardial leads exist, few postimplantation data have been reported. To compare "screw-in" (6917-35) leads with "stab-on" leads (4951-35) from the same manufacturer, we reviewed the records of 80 young patients (age 8 days to 29 years) who underwent ventricular epicardial pacemaker implantation from 1973 to 1986. Follow-up for the 57 patients with the 6917-35 model ranged from 3 months to 17 years (median 6.5 years) and for the 23 patients with the 4951-35 model 9 days to 4.25 years (median 2.0 years). Actuarial life table analysis revealed significantly (P less than 0.001) fewer 4951-35 leads were functioning at each of 1-5 years after implant, compared to the 6917-35 leads. Analysis of available threshold pulse width data revealed no difference (P = 0.08) acutely (6 weeks after implant), but a significantly (P = 0.05) higher mean threshold for the 4951-35 leads was found chronically. No significant correlation was found for lead failure with age, underlying heart disease, lead site (i.e., left or right ventricle), or surgical approach. Using the sutureless, stab-on technique, the 4951-35 lead is associated with higher thresholds and lower survival rate when compared to the 6917-35 lead.     

Programmable Polarity: Effects on Pacing and Sensing of Bipolar Steroid-Eluting Leads

Presently available bipolar pacemakers connected to bipolar leads allow the programming of polarity to either bipolar or unipolar configuration. The bipolar configuration improves sensing because of its lack of oversensing. In respect to the pacing impulse, it may be beneficial to program the bipolar to unipolar configuration, because the unipolar pacing configuration seems to lead to lower pacing thresholds. The aim of the study was to investigate the effects of the two configurations on pacing and sensing in 11 patients with a new ventricular steroid-eluting lead (Encor Dec 033–301. Telectronics Inc.) connected to the same types of VVI(R) pacemakers. Follow-up was 12 months after implantation. Pacing was assessed by pulse duration thresholds at 0.8-, 1.6-, and 2.5-V pulse amplitude and by pacing impedance. Parameters for sensing included sensing thresholds, R wave amplitudes, and amplitude of intrinsic deflection. Pulse duration thresholds were similar for the two configurations. At implantation, pacing impedance was significantly higher with bipolar (672 ± 60 Ω) than with unipolar pacing configuration (626 ± 82 Ω, P < 0.005). The difference lasted until 1 month after implantation (bipolar: 670 ± 49 Ω: unipolar: 630 53 Ω, P < 0.01). No significant differences were detected after 3 (bipolar: 683 ± 63 Ω; unipolar: 662 ± 70 Ω) and 12 months (bipolar: 658 ± 64 Ω: unipolar: 660 ± 63 Ω) between the 2 configurations. Although intrinsic deflections of ventricular electrograms were different, mean R wave amplitudes were similar in unipolar and bipolar configuration. Pacing and sensing characteristics of unipolar and bipolar configuration were similar for the studied bipolar pacing lead. Pacing impedance was initially higher for bipolar than for unipolar configuration and equilibrated within 3 months after implantation.     

Long-Term Follow-Up of Patients Treated with Automatic Scanning Antitachycardia Pacemaker

The long-term efficacy of an automatic antitachycardia pacemaker was evaluated in 13 patients with supraventricular tachycardia and in two patients with ventricular tachycardia. Patients were followed for 4–53 months (median 16). The concertina scanning mode with 2–7 extrastimuli proved to be effective in all patients but one. During follow-up, two patients had to be reoperated due to sensing problems. Atrial flutter was induced during scanning in one patient, termination mode was triggered by sinus tachycardia in one patient despite beta blocker therapy, and in one patient after cessation of beta blocker treatment. The pacemaker did not induce any serious arrhythmias and no sudden deaths occurred. Seven patients were given beta blockers, one patient with ventricular tachycardia was additionally administered amiodarone. In conclusion, the PASAR 4171 (Telectronics, Englewood, CO, USA) automatic scanning pacemaker is an alternative or adjunctive means to chronic antiarrhythmic drug therapy in patients with supraventricular tachycardia, but further versatility with regard to sensitivity, refractory period, and tachycardia recognition is required to eliminate the shortcomings observed, including the need for additional beta blocker therapy.     

Percutaneous Removal of Infected Permanent Pacemaker Leads Using a Simple Coaxial Dilating System

A simple traction-countertraction technique using common and readily available materials was successfully used to remove infected pacemaker leads from two patients. The specific methodology is presented. Although somewhat technically demanding, this approach appears safe and cost-effective. This method provides another way to remove pacemaker leads without resorting to thoracotomy.     

Pacemaker Follow-Up: Its Role in the Detection and Correction of Pacemaker System Malfunction

The goal of pacemaker follow-up is not only to detect battery depletion but also to detect all malfunctions of the pacing system and, when possible, to correct such problems using programming. During one year, we discovered 61 such malfunctions in a clinic of 1065 patients (5.7%). These were more frequent in the first year (7.7%) than in the third to fifth years of follow-up (range 3.1-4.8%). The incidence rose again in the sixth and subsequent years (7-7.7%). Despite a significant occurrence of malfunctions (5.2%) among multiprogrammable pacemakers, the necessity for operative intervention for their correction was low (1.2%). Sensing problems were the most common (57%) and the most likely to be corrected by reprogramming (85%); problems involving loss of capture were less likely to be corrected by programming (38.5%). Battery depletion accounted for only 18% of malfunctions, occurring earliest in the forty-third month of follow-up. Pulse generator longevity of those devices reaching end of battery life during the study period was 68.6 +/- 16.7 months (mean + SD). We conclude that specialized pacemaker follow-up continues to be necessary despite improved pulse generator reliability and longevity. Indeed, with reprogramming, it presently plays an even more important role than in the past. Follow-up should be oriented not only to the detection of battery depletion but also toward a comprehensive surveillance of pacemaker system function.     

Ambulatory Electrocardiography for the Detection of Pacemaker Lead Failure

The suboptimal performance of some polyurethane bipolar pacing leads has highlighted concern about the optimal method of monitoring pacemaker lead performance. Since the manifestations of premature lead failure may be initially intermittent, we hypothesized that ambulatory electrocardiography (AECG) would be a more sensitive tool for the detection of pacing lead failure compared to increased pacemaker clinic surveillance. Since the Medtronic safety alerts on the 4012, 4082, and 4004 leads, we have followed 261 patients by serial AECG and 165 patients by increased pacemaker clinic surveillance. Lead failures were identified in 75 patients: 68 in the AECG group (31 %) and 7 in the clinic group (4%, P < 0.001). Repeat AECG confirmed the lead failure in 38 (97%) of 39 patients in which it could be done. Pacing lead failure documented by AECG could be confirmed by a subsequent clinic assessment in only 15 (25%) of 60 patients evaluated (P < 0.001). The actuarial survival of the 4012 lead was significantly lower in the AECG group compared to the clinic group (56% vs 87% survival at 8 years, P < 0.002). Similar trends were observed for the 4082 and 4004 leads. AECG is a more sensitive method of surveillance for pacemaker lead function compared to pacemaker clinic assessment. AECG should be incorporated into the routine follow-up of pacemaker patients. (PAGE 1997; 20[Pt. I]:127 4-1282)     

Perforation of the Right Ventricle by Transvenous Defibrillator Leads: Prevention and Treatment

A series of 78 consecutive implants of the transvene PCD (Medtronic, Inc.) defibrillator system is presented and the occurrence of right ventricular perforation in 4 patients reported (5.2%). Diagnosis of perforation is made using four signs: (1) decrease in arterial blood pressure without any other explanation; (2) decrease in pulsatility of the cardiac silhouette as monitored by fluoroscopy; (3) increased size of the cardiac silhouette; and (4) abnormal position of the transvenous lead too far out toward the left ventricle along the pericardial outline. Perforation causes rapid and dramatic cardiac tamponade due to the large diameter and stiffness of the coil carrier lead. Immediate drainage of the hemopericardium must be carried out using the transxiphoid approach. The use of a thin blue-coded lead stylet (0.014-inch gauge) is recommended over the stiffer maroon-coded stylet. Since treatment must be carried out immediately, it is advised that a surgeon either perform, assist, or be immediately available whenever one of these systems is implanted.